This invention relates to a process of treating a liquid waste containing organic matters and nitrogen-and/or phosphorus-containing inorganic matters by anaerobic digestion of the organic matters.
Anaerobic digestion with fermentation bacteria and methane-producing bacteria has been hitherto used for treating waste water containing organic matters, because the process can be performed at low costs and can yield methane useful as an energy source. One problem of this process is that nitrogen- and/or phosphorus-containing inorganic matters which would cause eutrophication of sea, lake, etc. are hardly treated.
JP-B-H7-96118 discloses a method of treating a waste water in a reactor having a packed bed of ceramic carrier particles supporting thereon phototrophic bacteria and methane-producing bacteria. The waste water is passed through the packed bed in the reactor maintained under anaerobic conditions, while irradiating the packed bed with light. This method has a problem because a large amount of bacteria cannot be supported on the ceramic carrier and because nitrogen compounds are not efficiently removed. Additionally, the use of the carrier requires an increased cost.
Phototrophic bacteria are useful for the production of hydrogen and valuable chemical compounds such as raw materials for biodecomposable plastics and oleic acid. Further, phototrophic bacteria may be utilizable as fodder and fertilizer. Thus, there is a great demand for techniques for proliferating phototrophic bacteria in an economical manner.